Non-negotiable but you can use the referral credit on inventory models.Are prices on CPO cars or new inventory cars negotiable or potentially depend on who you talk to at Tesla? How complete or up to date is the inventory list on the Tesla website?
What are you looking for exactly? At teslainventory.com, you can see there are currently 36 inventory models with discounts of $10000 or more. Currently there are over 160 with disccounts between $200 and $13600 off. The referral credit would shave another $1000 off inventory models but you'd have to give the code to your Owner Advisor since you can't use the referral link directly if you place the order for an inventory model online.
Tesla constantly updates the inventory listed on their site. They do have many CPO models which they don't have listed on their site.